The 3GPP Release-5/6/7 specifications define HSDPA with adaptive modulation where the used modulation is either QPSK or 16QAM depending on the Node B scheduler decision for providing communication in for example, a cellular telecommunications system such as schematically represented in FIG. 1 and generally designated 4. Recently there has been discussion on also introducing the possibility of using 64QAM with HSDPA in 3GPP. At the same time, 3GPP is specifying a MIMO (multiple input-multiple output) multi-antenna technique for HSDPA MIMO which requires some redesign for the HSDPA related control channels.
With reference to FIG. 2, the current HS-SCCH structure used to inform the format of the actual HS-DSCH transmission (including the used modulation) is split to two parts. HS-SCCH Part 1 contains 8 bits of which 7 bits are used to inform the used HS-PDSCH codes for the HS-DSCH transmission and one bit is used to inform or identify the modulation (QPSK/16QAM) used on those HS-PDSCH codes. HS-SCCH Part 2 provides further information for example, transport block size, HARQ information, etc.
The reader is referred to the literature in the art and numerous text references for a further understanding of HSDPA such as found for example in Chapter 12 of the text titled “WCDMA Requirements and Practical Design” published by Wiley, and which is incorporated herein by reference.
Still considering FIG. 2, the HS-SCCH transmission starts 5120 chips earlier than the HS-DSCH transmission in order to allow the user equipment (UE) receiver to get the first part (part 1) of the HS-SCCH before the HS-DSCH reception starts and thus to know in advance the codes and modulation used on the HS-DSCH.
Now with the added requirement of HSDPA MIMO, the intention is to further add two bits of the antenna weights used for the HS-DSCH transmission to HS-SCCH part 1 and one bit indicating the number of streams, one or two, used in the downlink's transmission (a rank-indicator bit) to also provide this MIMO specific information to the receiver. Part 1 of HS-SCCH structure therefore would be required to carry either 8 bits or 11 bits depending on whether MIMO is in use or not. As a consequence of the HSDPA MIMO requirement, two different HS-SCCH Part 1 formats must be specified.
The problem that must now be solved is how to add a new modulation (64QAM) indication to the part 1 of the HS-SCCH structure.
Ericsson's R1-062935 in 3GPP RAN1 meeting #46bis in October 2006, entitled “Higher Order Modulation for HSPA-Impact on RAN1 specifications” which is incorporated herein by reference suggests using the same approach as was done with the antenna weight bits with MIMO, that is, to make room for one additional bit to the part 1 of the HS-SCCH structure by reducing the error correction coding of the part 1. The approach described by Ericsson for adding a new modulation indication to the HS-SCCH part 1 for identifying 64QAM modulation is not satisfactory because a further additional bit must be added to the HS-SCCH part 1 structure.
The disadvantages of adding a new modulation bit to the HS-SCCH first part for 64 QAM or HSDPA MIMO operation include at least the following concerns that make the proposal unacceptable:
1) two new HS-SCCH formatted structures are required in addition to the other two HS-SCCH formatted structures. The number of HS-SCCH formats would be doubled to 4 different HS-SCCH formats to cover the situations with/without MIMO and with/without 64QAM support and would require additional buffering to determine the modulation indication to distinguish between 16QAM modulation and 64QAM modulation, and
2) there would be a reduction in the coding protection of the HS-SCCH part 1 as less error correction coding can be applied resulting a non-negligible impact to the performance.
What is needed is a single HS-SCCH structure that allows for the introduction of 64QAM modulation indication without requiring additional room for bits in the HS-SCCH part 1 structure to provide the 64 QAM modulation indication without requiring a different coding for the HS-SCCH when 64QAM modulation usage is enabled. or reducing the error correction coding that can be applied when 64 QAM modulation is enabled.